Crystal structures of three newly synthesized flavanone hydrazones

The crystal structures of racemic mixtures of three new flavanone-hydrazones are reported: (±,E)-N′-[5,7-dihydroxy-2-(4-hydroxyphenyl)chroman-4-ylidene]-2-(naphthalen-1-yl)acetohydrazide ethyl acetate monosolvate, (±,E)-N′-[5,7-dihydroxy-2-(4-hydroxyphenyl)chroman-4-ylidene]-4-hydroxybenzohydrazide ethanol monosolvate and (±,E)-N′-(6-methoxy-2-phenylchroman-4-ylidene)-2-(naphthalen-1-yloxy)acetohydrazide. All three hydrazones are in the E isomeric form and exhibit a pucker at the chiral carbon atom. The naringenin-derived hydrazones both show intramolecular hydrogen bonding between the hydrazone nitrogen atom and a hydroxy group on the chromane ring.

In II, the 4-hydroxyphenyl ring of the hydrazone moiety is coplanar with the chromane ring [dihedral angle of 2.485 (3) with the chromane ring system] whereas the other hydroxyphenyl ring is almost perpendicular [75.449 (5) ] to the chro- Asymmetric unit of II with displacement ellipsoids drawn at the 50% probability level.

Figure 3
Asymmetric unit of III with displacement ellipsoids drawn at the 50% probability level.

Figure 1
Asymmetric unit of I with displacement ellipsoids drawn at the 50% probability level. mane ring system. The chiral carbon of chromane ring (C8_1) and the methyl carbon (C2_1) of the solvent molecule show positional disorder. An intramolecular O-HÁ Á ÁN hydrogen bond exists between one of the hydroxy groups on the chromane ring and the nitrogen of the hydrazone group [O3-H3Á Á ÁN1 = 2.542 (3) Å , 147 ].
In III, the phenyl ring makes a dihedral angle of 86.17 (1) with the chromane ring system, while the naphthalene ring system is perpendicular to the chromane ring system [dihedral angle = 89.65 (1) ].

Supramolecular features
The extended packing of both I and II (Figs. 4 and 5) exhibit intermolecular O-HÁ Á ÁO and C-HÁ Á ÁO-type interactions. Additionally II has N-HÁ Á ÁO-type interactions (Tables 1 and  2). Both these packings have solvent molecules, namely ethyl acetate and ethanol, respectively, which interact with the parent molecules via O-HÁ Á ÁO-type hydrogen bonds. In I,interactions between the chromane rings of symmetryrelated neighbors in the [101] direction are observed. The hydroxyphenyl rings also show similar stacking with their symmetry-related counterparts along the [101] direction. Partial stacking (-) interactions [centroid-centroid distance = 4.51 (1) Å ] are observed between the chromane unit and the 4-hydroxyphenyl ring of the hydrazone moiety.

Synthesis and crystallization
For the preparation of I, naringenin (653 mg, 2.4 mmol) and 2-(naphthalen-1-yl)acetohydrazide (501 mg, 2.5 mmol) were dissolved in ethanol (10 mL). Acetic acid (2.4 mmol, 137 mL) was added and the resultant solution was heated at reflux for 21 h. The precipitate was isolated via vacuum filtration and recrystallized from ethyl acetate via slow evaporation at room temperature to furnish clear, plate-shaped crystals suitable for X-ray analysis.
For the preparation of II, naringenin (3.000 g, 11.02 mmol) and 4-hydroxybenzohydrazine (2.011 g, 13.22 mmol) were dissolved in ethanol (20 mL). Acetic acid (17.5 mmol, 1.0 mL) was added and the resultant solution was heated at reflux for 48 h. The precipitate was isolated via filtration and recrystallized from ethanol via slow evaporation at room temperature to furnish transparent yellow, plate-shaped crystals suitable for X-ray analysis.
For the preparation of III, 6-methoxyflavanone (381 mg, 1.5 mmol), 2-(naphthalen-1-yl)acetohydrazide (356.8 mg, 1.1 eq, 1.65 mmol), and p-toluenesulfonic acid (29 mg, 0.10 eq, 0.15 mmol) were dissolved in toluene (15mL). The resultant mixture was heated at reflux for 12 h with a Dean-Stark apparatus. The solvent was removed and the crude product was purified on an automated flash chromatography system using a normal phase silica gel column with a gradient of hexane:ethyl acetate (70:30 to 0:100). Recrystallization of the purified compound from ethanol via slow evaporation at room temperature furnished yellow, needle-shaped crystals suitable for X-ray analysis.

Special details
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

Special details
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.